Charged coupled devices (CCDs) have been in use for decades and are well known in the field of spectroscopy. Spectroscopy typically involves illuminating one or more rows of a CCD with the spectrum of a signal and then analyzing the captured spectrum represented by the varying magnitudes of charge which accumulate on the various elements of the CCD. For example, if one row of the CCD is used to capture the spectrum, the varying magnitudes of charge along the row represent the varying amplitudes of different wavelengths which comprise the spectrum.
The use of CCDs in spectroscopy may be divided into at least two well known types: multiline spectroscopy and kinetic spectroscopy. Commercially available CCDs are usually extremely application specific, and typically are manufactured for use in either multiline spectroscopy, kinetic spectroscopy, or some other application. Conventional CCDs include little or no ability to adapt to different applications.
Kinetic spectroscopy involves obtaining multiple spectra, one at a time, at a relatively high rate, and then reading them from the CCD. FIG. 1 shows a conceptual diagram of a CCD for use in kinetic spectroscopy. The first row of elements 101 is utilized to capture a spectrum by focusing the desired spectrum only on row 101. After the spectrum is captured at row 101, it is shifted down to row 102 immediately below row 101 and the next spectrum is captured at row 101. In one commercially available CCD, all rows except the top row 101 are masked. Thus, once the spectrum is captured and shifted down into row 102, it is no longer subject to distortion from unwanted light signals and the masked rows operate effectively as a memory. Utilizing, for example, an off the shelf 1024.times.256 CCD 100 of the type described, approximately 65,000 spectra per second may be collected for subsequent read-out through horizontal register 103 and amplifier 104.
Although the arrangement shown in FIG. 1 has been widely accepted in the prior art for performing kinetic spectroscopy, there are drawbacks to such an arrangement. First, since only one row of CCD elements is typically utilized to capture the spectrum, the device is not very sensitive. If the spectrum is focused on plural rows of CCD elements, the device will be more sensitive, however, the read out time will increase dramatically since a spectrum occupying N rows of elements will require N times the read out time when compared with a spectrum occupying one row. The slower read out time is unacceptable in certain applications.
Another problem with the arrangement described is that it is relatively inflexible. Specifically, the CCD with all of its rows except one masked is not suitable for multiline spectroscopy, described below. More particularly, multiline spectroscopy requires several spectra to be captured simultaneously. The availability of only one row of unmasked elements in the arrangement of FIG. 1 is unsuitable. Thus, if the specific application changes, a whole new design is required.
In view of the above, it can be appreciated that there exists a need in the art for a more sensitive CCD based device which is able to capture and read out spectra at a fast rate for use in kinetic spectroscopy, and which is flexible enough to be adapted for different uses.
Multiline spectroscopy is another branch of spectroscopy which is often implemented using CCD devices. FIG. 2 shows a conceptual diagram of a CCD being utilized to effectuate multiline spectroscopy.
In multiline spectroscopy, several separate and distinct spectra are captured by a CCD and read out separately for analysis through horizontal shift register 210. The plural spectra are usually captured simultaneously, and then later shifted out of the CCD sequentially for storage and analysis. The arrangement in FIG. 2 includes such a charge coupled device 200, a plurality of exemplary spectra represented by 201 through 204, and a horizontal register 210 for reading out the spectra. Additionally, the regions 205 through 208 represent separation bands in order to prevent energy from each distinct spectrum from contaminating the energy in the regions storing the other spectra.
In operation, the spectra are first captured on the CCD 200, perhaps with the use of a mechanical shutter. Next, the spectra are read by placing them into horizontal register 210 and then shifting each spectrum from register 210 for later storage, analysis or any other required processing.
A problem with the use of arrangements such as that of FIG. 2 to accomplish multiline spectroscopy is that the dark bands 205 through 208 must be independently read into horizontal register 210 and shifted out. Accordingly, the overall operation of the device is much slower than desirable.
Another problem with the arrangement of FIG. 2 for multiline spectroscopy is that if it is desired to utilize the same chip for kinetic spectroscopy, a large waste in space and time results. Specifically, FIG. 6 shows a conventional CCD device 601 and includes a representation 602 of a single spectrum stored in one row of the device. In operation, the spectrum 602 is transferred into horizontal register 603 for shifting out. The dark charge from region 603 must then also be shifted out. This results in wasted time and thus, slower throughout.
Alternatively, when a device is being utilized to capture single spectrum using the technique described, an arrangement such as that shown in FIG. 7 may be used. The arrangement of FIG. 7 includes a relatively small CCD for capturing a single spectrum and a horizontal register 702 for the read out of such spectrum. However, if it is later desired to do multiline spectroscopy utilizing a larger CCD device, the entire chip would have to be replaced.
In view of the above there exists a need in the art for an improved CCD arrangement for performing multiline and kinetic spectroscopy. Additionally, such device should be adaptable easily for either of the foregoing types of spectroscopy and should be efficient when operated in either mode. Finally, there exists a need for improved speed when performing either type of spectroscopy utilizing CCD devices.